1. Field of the Invention
The present invention generally to controlling a power train that includes an engine and a continuously variable transmission. More specifically, the present invention relates to an engine rotational speed control apparatus for a power train that improves fuel efficiency when a requested output of the engine increases or decreases.
2. Background Information
Engines are sometimes provided with a control apparatus that is designed to improve fuel efficiency (i.e., reduce fuel consumption). An example of a conventional engine control technology is disclosed in Japanese Laid-Open Patent Publication No. 2003-035191 that is designed to improve fuel efficiency of an engine. In this conventional technology, the engine rotational speed is controlled by controlling a gear ratio of a continuously variable transmission in response to any given engine output power request such that the engine rotational speed lies on an optimum fuel efficiency operation curve made up of optimum fuel efficiency operating points. The optimum fuel efficiency operating points are based on an engine torque and an engine rotational speed at which a requested engine output can be achieved with a minimum fuel consumption. In other words, the conventional technology controls the engine rotational speed such that the requested engine output is always delivered using an optimum fuel efficiency operating point lying on the optimum fuel efficiency operation curve.